Wednesday, November 2, 2011

Supercomputers Used to Analyze Stockpile-to-Target Sequence in Nuclear Weapons

A group of nuclear weapons designers and scientists at the Lawrence Livermore National Laboratory conducted a what-if experiment several years ago, deploying supercomputers to simulate what happens to a nuclear weapon from the moment it leaves storage to the point when it hits a target.

They methodically worked down a checklist of all the possible conditions that could affect the B-83 strategic nuclear bomb, the most powerful and one of the most modern weapons in the U.S. arsenal, officials said. The scientists and designers examined how temperature, altitude, vibration and other factors would affect the bomb in what is called the stockpile-to-target sequenceSuch checks typically have been carried out by taking bombs and warheads apart; scrutinizing them using chemistry, physics, mathematics, materials science and other disciplines; and examining data from earlier nuclear explosive tests. This time, however, the scientists and designers relied entirely on supercomputer modeling, running huge amounts of code.

Then came a surprise. The computer simulations showed that at a certain point from stockpile to target, the weapon would “fail catastrophically,” according to Bruce T. Goodwin, principal associate director at Livermore for weapons programs. Such a failure would mean that the weapon would not produce the explosive yield expected by the military — either none at all, or something quite different than required to properly hit the target.

“So we went in and thoroughly investigated that, and determined that the way the weapon is handled by the military had to be changed, or you would be susceptible to having the weapons fail catastrophically when, God forbid, they should ever be used,” Goodwin said. He added that the fault occurred in the “real dynamics of the vehicle” — a term describing the weapon’s trajectory and behavior — and could not have been revealed by underground explosive testing or by examining the components.

Following the discovery and a multi-year effort, the B-83 bombs and the military’s handling procedures for the weapons have been fixed, officials said.